1. Field of the Invention
The present invention relates to circuit board structures and fabrication methods thereof, and more particularly, to a circuit board structure having at least an embedded electronic element and a fabrication method thereof.
2. Description of Related Art
Along with the progress of semiconductor packaging technologies, various package types have been developed for semiconductor devices. For example, an electronic element can be embedded in and electrically connected to a packaging substrate so as to form a package. Such a package has reduced size and improved electrical performance and therefore has become a main trend.
FIGS. 1A to 1F are schematic cross-sectional views showing a circuit board structure having embedded electronic elements and a fabrication method thereof according to the prior art.
Referring to FIG. 1A, a substrate 10 is provided, which has opposite first and second surfaces 10a, 10b and a cavity 100 penetrating the first and second surfaces 10a, 10b. An adhesive layer 11 is formed on the second surface 10b of the substrate 10 to cover one end of the cavity 100, and a plurality of electronic elements 12 are disposed on the adhesive layer 11 in the cavity 100. Each of the electronic elements 12 has a first active surface 12a having a plurality of first electrode pads 121a and a second active surface 12b opposite to the first active surface 12a and having a plurality of second electrode pads 121b. The first active surfaces 12a and the first electrode pads 121a of the electronic elements 12 are exposed from the first surface 10a of the substrate 10.
Referring to FIG. 1B, a first dielectric layer 13a is laminated on the first surface 10a of the substrate 10 and the first active surfaces 12a of the electronic elements 12. Further, the first dielectric layer 13a flows into the cavity 100 so as to cover side surfaces of the electronic elements 12.
Referring to FIG. 1C, the adhesive layer 11 is removed to expose the second active surfaces 12b and the second electrode pads 121b of the electronic elements 12 from the second surface 10b of the substrate 10. Then, a second dielectric layer 13b is laminated on the second surface 10b of the substrate 10 and the second active surfaces 12b of the electronic elements 12. Thereafter, the first dielectric layer 13a is covered with a first copper foil 14a, and the second dielectric layer 13b is covered with a second copper foil 14b. 
Referring to FIG. 1D, a brown oxide treatment is applied to the first and second copper foils 14a, 14b, and a laser drilling process is performed to form a plurality of first openings 130a through the first copper foil 14a and the first dielectric layer 13a to expose the first electrode pads 121a and form a plurality of second openings 130b through the second copper foil 14b and the second dielectric layer 13b to expose the second electrode pads 121b. 
Referring to FIG. 1E, a conductive layer 15 is formed on walls of the first and second openings 130a, 130b by electroless plating.
Referring to FIG. 1F, an electroplating process is performed through the conductive layer 15 so as to form a plurality of first conductive vias 16a in the first openings 130a and form a plurality of second conductive vias 16b in the second openings 130b, thus electrically connecting the first and second copper foils 14a, 14b through the first and second conductive vias 16a, 16b. 
However, in the above-described method, the laser drilling, electroless plating and electroplating processes are complicated, costly and time-consuming.
Therefore, there is a need to provide a circuit board structure having at least an embedded electronic element and a fabrication method thereof so as to overcome the above-described drawbacks.